Aircraft Comprising At Least One Net For Reducing Aerodynamic Noise From A Structural Element Of Said Aircraft

ABSTRACT

The invention relates to an aircraft comprising at least one net for reducing aerodynamic noise from a structural element of said aircraft. According to the invention, the flexible net ( 5 A) associated with the structural element ( 2 ) is retractable and capable of occupying at least one position located between the following two end positions: a deployed position, in which the net is placed in a turbulence area (T), and a retracted position, in which said net ( 5 A) is at least partially outside said turbulence area (T).

The present invention relates to an aircraft comprising at least one netfor reducing aerodynamic noise from a structural element of saidaircraft generated upon a movement of the latter.

It is known that there are numerous sources of noise on an aircraft, forexample, a transport airplane, generated by an air flow aroundstructural elements of the aircraft, either stationary (for instance thesuspension struts, the wings, etc.) or mobile (for instance the leadingedge slats, the trailing edge flaps, the airbrakes, etc.). Indeed, theinteraction of such air flow with a structural element creates aturbulence area in the vicinity of the downstream part of said element,generating alone or thru an interaction with another auxiliarystructural element of the aircraft arranged within said turbulence area,undesirable aerodynamic noise.

In order to reduce the generated noise strength, it is known to arrangea net with geometric meshes in the vicinity of the downstream part ofsaid structural element, within the turbulence area. Thus, theturbulences crossing the net are broken so that they lose the substanceof their energy, thus leading to a reduction of the aerodynamic noisestrength.

However, the presence of such noise reduction net on a structuralelement can highly degrade the performances of the aircraft upon someflight phases, including these for which a noise reduction is notnecessary (for example, a cruising flight).

The object of the present invention is to remedy such disadvantage andincluding to avoid that the noise reduction net(s) substantiallydegrade(s) the performances of the latter upon a flight.

To this end, according to the invention, the aircraft comprising:

-   -   at least one aerodynamic structural element arranged in an air        flow, said air flow around said element generating, at least on        one of the ends thereof, a turbulence area at the origin of the        noise; and    -   at least one flexible net arranged on such end of said element,        for reducing at least partially said generated noise,        is remarkable in that said flexible net is retractable and can        occupy at least one position comprised between the two following        extreme positions:    -   one extended position in which said flexible net is arranged        within said turbulence area; and    -   one retracted position in which said flexible net is at least        partially outside said turbulence area.

Thus, thanks to the invention, the flexible net can be extended in theturbulence area at the origin of the undesirable aerodynamic noise, soas to reduce it upon given flight phases (approach, take off, etc.). Itcan further be retracted upon some flight phases of the aircraft(climbing, cruising, etc.), when it has no utility any longer so as toavoid a degradation of the performances of the aircraft.

Advantageously, the position of said net is automatically adaptable as afunction of at least one parameter of said aircraft (for example, speed,altitude, incidence, etc.).

In particular, said net can be adaptive, i.e. the position adaptation ofthe latter is automatically performed under the only action of said airflow (and thus of the speed of said aircraft).

Furthermore, the aircraft can include extension means for said net(being adapted for example to be formed by the structural element itselfwhen it is mobile), intended to extend and retract the latter. Suchextension means can for example be manually controlled by the pilots or,on the contrary, automatically.

Preferably, in the retracted position, said net can be either housed atleast partially in said element, or even pressed against at least onewall of the latter.

Moreover, when it occupies said retracted position, said net canadvantageously be folded on itself.

In order to even optimize the noise reduction, said net can, in anextended position, present an optimized cross-section of the concaverounded type with respect to said air flow.

The FIGS. of the accompanying drawing will make well understood how theinvention can be implemented. On such FIGS., identical references denotesimilar elements.

FIG. 1 shows, in a top partial schematic view, an airplane wingcomprising a retractable noise reduction net according to a firstexemplary embodiment of the invention. In such example, the net is usedto break the turbulences formed by an air flow around a leading edgeslat of the wing.

FIG. 2 is a cross-sectional view of the wing of FIG. 1 along the lineII-II.

FIG. 3 is a profile schematic view of a suspension strut in a turbopropwith propulsive propeller provided with a retractable noise reductionnet according to a second exemplary embodiment of the invention.

FIG. 4 is a schematic cross-sectional view of the strut of FIG. 3 alongthe line IV-IV.

FIGS. 5 to 8 are variations of the example illustrated on FIG. 4.

FIG. 9 is a cross-sectional view of an aircraft wing comprising aretractable noise reduction net according to a third exemplaryembodiment of the invention, being intended to weaken the turbulencesformed by an air flow around an airbrake mounted on the wing.

FIG. 10, similar to FIG. 9 shows a retractable noise reduction netaccording to a fourth exemplary embodiment of the invention to reducethe turbulences formed on the longitudinal end of a wing airbrake of anairplane.

On FIGS. 1 and 2, according to the first exemplary embodiment of theinvention, there is illustrated an airplane wing 1 provided with aleading edge slat 2 and a trailing edge flap 3, both being mobile.

As shown on FIG. 2, the slat 2 is represented in a continuous line, whenit is integrally retracted, and in a discontinuous line when it occupiesa partially extended position.

In an integrally extended position, an air flow (symbolized by the arrowE) around the slat 2 generates a turbulence area T in the vicinity ofthe downstream part of the latter. The upstream part 4 of the wing 1,being arranged in the downstream extension of the extended slat 2, isthen immersed at least partially in the turbulence area T. Theinteraction of the turbulences with the upstream part 4 of the wing 1causes aerodynamic noise, which is in particular undesirable upon anapproach or a take off phase.

According to the invention, to reduce at least in part such undesirableaerodynamic noise, a noise reduction net 5A is arranged between the slat2 and the upstream part 4 of the wing 1, thereby breaking theturbulences being formed and reducing the noise strength on such a way.The net 5A extending longitudinally between the slat 2 and the wing 1 isfastened, on the one side, to the undersurface 2A of said slat 2 and, onthe other side, to the opposite upstream part 4.

The net 5A, for example made with geometric meshes, is flexible andfoldable. It can occupy at least one intermediate position between thetwo following extreme positions:

-   -   one extended position in which it is arranged in said turbulence        area T (the net 5A is represented in a continuous line in this        position on FIG. 2). Such an extended position corresponds to an        integral extension of the slat 2; and    -   one retracted position in which said net 5A is outside said air        flow E. Such a retracted position coincides with an entirely        folded position of the slat 2 on the wing 1. In such retracted        position, the net 5A is folded on itself at least one time        toward the undersurface 2A of the slat 2. It is moreover pressed        against the latter.

On FIG. 2, the net 5A is also represented in a discontinuous line in anintermediate position between the two above mentioned extreme positions,in association with a partial extension of the slat 2.

As the net 5A is an integral part of the slat 2, the extension of thelatter (manually controlled by the pilots or automatically) causes theextension of the net 5A. It is the same for the folding of the net 5A.It other words, the leading edge slat 2 plays the role of extensionmeans for the net 5A.

In the second exemplary embodiment according to the invention andillustrated on FIGS. 3 and 4, a suspension strut of a turboprop 8 withpropulsive propeller 9 mounted under an airplane wing 1 is considered.An airflow E around the strut 7 leads to the formation of a turbulencearea T in the vicinity of the downstream end 7A of said strut 7 which,when it interacts with the propeller 9 arranged downstream from thelatter, generates undesirable noise.

Thus, according to the invention, in order to reduce the noise beinggenerated, a retractable net 5B is arranged at the level of thedownstream end 7A of the suspension strut 7. It extends along the latterfor example over at least one part of the height thereof.

Moreover, the net 5B is able to occupy at least one position between thetwo following extreme positions:

-   -   one extended position where it is arranged within said        turbulence area T (the net 5B is represented in a continuous        line in such latter position on FIG. 4). In this case, the net        5B being substantially plane is arranged on the rear of the        strut 7, in the extension of the leading edge 7B of the latter,        to reduce the pressure jump downstream from the strut 7.        Alternatively, the net 5B could be extended orthogonally to the        median vertical plane M passing thru the strut 7 (FIG. 5) and        possibly present an optimized shape (FIG. 6) for example with a        rounded concave cross-section with respect to the air flow E, so        as to reinforce the reduction of the aerodynamic noise. In        another variation illustrated on FIG. 7, the plane net 5B could        be, in an extended position, slanted with respect to the medium        vertical plane M of the strut 7;    -   one retracted position where the net 5B is inserted within a        housing 8 provided to this end in the downstream part 7A of the        strut 7 (the net 5B is represented in the retracted position in        a discontinuous line). The net 5B is thus outside the air flow E        and the turbulence area T.

The operations of extension and retraction of the net 5B within thehousing 8 are performed by extension means (not represented on theFIGS.), that could be automatically controlled as a function of anairplane parameter (for example speed, altitude, flight phase, etc.) or,on the contrary, manually by a voluntary action of the pilots.

In another variation of the second exemplary embodiment represented onFIG. 8, two adaptive nets 5C, extending along the strut 7, are arrangedrespectively on the downstream end of the external side walls 7B of thestrut 7. Each net 5CD is fastened to the corresponding side wall 7B viathe upstream end 9 thereof.

The adaptive net 5C are held in an extended position for which they rearranged in the turbulence area T (thru extension means for example ofthe elastic type do that, in the absence of an airflow E) the airplanespeed is then nil) they spontaneously occupy the extended position.

Moreover, depending the airplane speed and under the action of theairflow E, the nets 5C are able to occupy a plurality of intermediatepositions between the extended position and a retracted position (inwhich each net 5C is pressed against the corresponding side wall 7B ofthe strut 7). Thus, the higher the speed of the airplane, the bigger theair flow E on the nets 5C and the lesser the latter are extended.

On such a way, an automatic adjustment of the position of the nets 5C asa function of the airplane speed (a speed threshold can be implemented)is performed so as to avoid a degradation of the performances of thelatter during the flight (including upon a cruising phase) whilereducing aerodynamic noise when it is useful (for example upon a takeoff or an approach phase).

Furthermore, on FIG. 9, there are illustrated according to the thirdexemplary embodiment of the invention, a cross-section of the aircraftwing 1 provided with a trailing edge flap 3 and an airbrake 10(represented in an extended position).

In order to reduce the turbulences T formed by an aerodynamic flow Earound the airbrake 10 being extended, a retractable net 5D is arranged,longitudinally extending along said wing 1 on the downstream end 6 ofthe latter.

The extension of the net 5D from a retracted position (the net 5D isrepresented in a discontinuous line), in which it is inserted in ahousing 8 arranged in the downstream part 6 of said wing 1, to anextended position (the net 5D is represented in a continuous line), inwhich it is arranged in the turbulence area T, can be related to theextension of the flap 3 of the airbrake 10. Such an extension of the net5B can be obtained thru extension means (not represented).

According to the fourth exemplary embodiment, a foldable net 5E can bearranged on each of the two longitudinal ends of the airbrake 10A. Whenthe airbrake 10 is extended, the nets 5E occupy an extended position(FIG. 10) and, when the airbrake 10 is retracted, the nets 5E are foldedon themselves in a retracted position (not represented). The airbrake 10is then used as extension means for the nets 5E.

On such a way, the noise generated on the longitudinal ends of theairbrake 10 (also called “corner noise”) can be reduced.

1. An aircraft comprising: at least one aerodynamic structural element(2, 7, 10) arranged in an air flow (E), said air flow around saidelement generating, at least on one of the ends thereof, a turbulencearea (T) at the origin of the noise; and at least one flexible netarranged on such end of said element (2, 7, 10), for reducing at leastpartially said generated noise, wherein said flexible net (5A to 5E) isretractable and can occupy at least one position comprised between thetwo following extreme positions: one extended position in which saidflexible net (5A to 5E) is arranged within said turbulence area (T); andone retracted position in which said flexible net (5A to 5E) is at leastpartially outside said turbulence area (T).
 2. The aircraft according toclaim 1, wherein the position of said net (5A to 5E) is automaticallyadaptable as a function of at least one parameter of said aircraft. 3.The aircraft according to claim 2, wherein the position adaptation ofsaid net (5C) is automatically performed under the only action of saidair flow (E).
 4. The aircraft according to claim 1, wherein it comprisesextension means (2, 10) of said net (5A, 5E).
 5. The aircraft accordingto claim 1, wherein, in a retracted position, said net (5B) is housed atleast partially in said structural element (7).
 6. The aircraftaccording to claim 1, wherein, in a retracted position, said net (5C) ispressed against at least one wall (7A) of said structural element (7).7. The aircraft according to claim 1, wherein net (5A, 5E) is able to befolded on itself when it occupies said retracted position.
 8. Theaircraft according to claim 1, wherein, in an extended position, saidnet (5B) presents an optimized cross-section of the concave rounded typewith respect to said air flow (E).